1) Field of the Invention
This invention relates to a double-sided printing apparatus and a double-sided printing method suitable for use for printing on front and rear surfaces of continuous recording paper, for example, by an electrophotographic method.
2) Description of the Related Art
In recent years, in a field of development of printers for continuous recording paper (a continuous medium), various double-sided printing apparatus have been placed on the market from various manufacturers. A double-sided printing apparatus is an apparatus for printing on both of the front surface and the rear surface of continuous recording paper by an electrophotographic method and includes two printers each of which can print on one surface of continuous recording paper and are connected to each other via a turn bar for turning over the continuous recording paper.
FIG. 12 is a schematic view of a double-sided printing apparatus. Referring to FIG. 12, the double-sided printing apparatus 80 shown includes a pair of printers 80a and 80d, a turn bar 80b, and a transport relaying apparatus 80c. Continuous recording paper 100 is printed on the front surface thereof by the printer 80a and turned over by the turn bar 80b. Then, the continuous recording paper 100 is transported through the transport relaying apparatus 80c and then printed on the rear surface thereof by the printer 80d. In this manner, the front and rear surfaces of the continuous recording paper 100 are printed by the two printers 80a and 80d which are connected to each other.
FIG. 13 is a schematic view of the printer 80d. The printer 80d shown in FIG. 13 prints on the rear surface of the continuous recording paper 100 discharged from the transport relaying apparatus 80c, and the continuous recording paper 100 released from the transport relaying apparatus 80c is loaded into the printer 80d. Then, the continuous recording paper 100 is transported by a tractor unit 95 which includes a pair of tractor belts 95a and 95c and a tractor motor 95b. During such transportation, toner powder sticking to a photosensitive drum 90e is transferred to the continuous recording paper 100 by a transfer charger (not shown) provided in the tractor unit 95 so that a print image is formed on the continuous recording paper 100. Then, the toner powder is fixed to the continuous recording paper 100 by heat in a flash fixing unit 91. Thereafter, the continuous recording paper 100 is stored into a paper folding unit 94b under the guidance of a pair of scuff rollers 92b and 92a. The scuff rollers 92b and 92a are rotating at an equalvelocity. A pair of pinch rollers 93a and 93b cooperate with the scuff rollers 92a and 92b, respectively, to transport the continuous recording paper 100.
As a mechanism for transporting the continuous recording paper 100, the tractor unit 95 shown in FIG. 13 serves as main transport means for transporting the continuous recording paper 100 and the scuff rollers 92b and 92a take up the continuous recording paper 100.
Meanwhile, toner power is transferred to a surface of the continuous recording paper 100 in accordance with a following flow. Referring to FIG. 13, the photosensitive drum 90e rotates in the clockwise direction. During rotation, the surface of the photosensitive drum 90e is first charged uniformly by a precharger 90c, and then, an electrostatic latent image of data to be printed is formed on the surface of the photosensitive drum 90e by exposure to light by an exposure station 90d. Then, the electro static latent image is developed into a toner image by a developing unit 90g, and the toner powder on the photosensitive drum 90e is transferred to the surface the continuous recording paper 100 by the transfer charger in the tractor unit 95. Meanwhile, remaining toner powder on the photosensitive drum 90e is removed by a cleaner station 90b. Then, the surface of the photosensitive drum 90e is charged uniformly by the precharger 90c again in order to prepare for a next transferring step.
Now, velocity variations of the tractor motor 95b in the tractor unit 95 and scuff motors in the scuff rollers 92b and 92a are described with reference to FIGS. 14(a), 14(b) and 15(a), 15(b), and also operation for keeping the tensile force of the continuous recording paper 100 is described. It is to be noted that the transport velocity of the tractor unit 95 is hereinafter referred to as main transport velocity, and the transport velocity of the scuff rollers 92b and 92a is hereinafter referred to as scuff transport velocity. Further, the direction along which the continuous recording paper 100 is printed and transported may be hereinafter referred to as forward direction or printing transport direction, and the direction opposite to the direction may be hereinafter referred to as reverse direction.
FIG. 14(a) is a diagram illustrating the velocity variation of the tractor motor upon starting of printing, and FIG. 14(b) is a diagram illustrating the velocity variation of the scuff motors upon starting of printing. The characteristic illustrated in FIG. 14(a) is a characteristic of the tractor motor 95b in the tractor unit 95, and the characteristic illustrated in FIG. 14(b) is a characteristic of the scuff motors (not shown) for driving the scuff rollers 92b and 92a. 
In a section denoted by A in FIG. 14(b), the scuff rollers 92b and 92a are started earlier than the tractor unit 95 to increase the tension of the continuous recording paper 100 (stretch the continuous recording paper 100 in a taut state). Also during printing, in order to assure a high tension to the continuous recording paper 100, the scuff transport velocity is set higher by approximately 5 to 30% than the main transport velocity.
FIG. 15(a) is a diagram illustrating the velocity variation of the tractor motor upon stopping of printing, and FIG. 15(b) is a diagram illustrating the velocity variation of the scuff motors upon stopping of printing. A velocity curve 90a shown in FIG. 15(a) indicates the main transport velocity. In FIG. 15(a), the tractor motor first rotates in the forward direction at a velocity V1 and then rotates reversely at another velocity xe2x88x92V2 after the velocity becomes equal to zero. Here, both of V1 and V2 are positive values. The reason why the rotation is reversed is that it is intended to adjust the printing position of the continuous recording paper 100 to a position suitable when next printing is to be started.
Meanwhile, the velocity curve 90bxe2x80x2 shown in FIG. 15(b) indicates the scuff transport velocity. The scuff transport velocity exhibits such a variation that the scuff motor continues to rotate forwardly at a velocity higher by approximately 5 to 30% than the main transport velocity and still continues its forward rotation even after the tractor unit 95 starts its backward transportation, and then stops after the tractor unit 95 stops its backward transportation. Therefore, in a section denoted by B in FIG. 15(b), the scuff rollers 92b and 92a rotate forwardly so that the continuous recording paper 100 is taken up by them and a predetermined tension of the continuous recording paper 100 is obtained thereby.
As described above with reference to FIGS. 14(a), 14(b), 15(a) and 15(b), the scuff rollers 92b and 92a operate to increase the tension of the continuous recording paper 100. In other words, they operate in such a manner as described in the following paragraphs {circle around (1)} to {circle around (3)}.
{circle around (1)} During printing, the scuff rollers 92b and 92a are set in an excessively feeding condition wherein the scuff velocity is higher by approximately 5 to 30% than the main transport velocity so that the continuous recording paper 100 may have a predetermined tension in order to prevent a slack (buffer) of the continuous recording paper 100. Consequently, good transportability and fixing stability of the continuous recording paper 100 are obtained in the flash fixing unit 91.
{circle around (2)} When transportation of the continuous recording paper 100 is started, the scuff rollers 92b and 92a are started earlier, for example, by approximately 3 seconds or more than starting of printing so that they may rotate but idly so that the continuous recording paper 100 may not become slackened thereby to assure transportability and fixing stability of the continuous recording paper 100 upon starting.
{circle around (3)} As an operation unique to the printer for continuous recording paper, upon stopping of printing, the continuous recording paper 100 stops after it is transported backwardly by approximately 1 to 4 inches. Also during such backward transportation, the scuff rollers 92b and 92a rotate forwardly so that the continuous recording paper 100 may have a predetermined tension at the flash fixing unit 91 thereby to make preparations for next printing.
Since the system described above merely requires control of the timings of starting and stopping and the velocities of rotation, it is advantageous in that an inexpensive scuff motor can be used and transportability and fixing stability of the continuous recording paper 100 are achieved.
Further, where the system described above is used for single-sided printing, no rubbing of the printed surface occurs in any case as described in the following paragraphs {circle around (4)} to {circle around (6)}.
{circle around (4)} While the scuff transport velocity during printing is higher by approximately 5 to 30%, since the pinch rollers 93a and 93b (refer to FIG. 13) which contact with the printed surface side of the continuous recording paper 100 are driven rollers and rotate at a velocity equal to the velocity at which the continuous recording paper 100 is transported, no stain to the print by rubbing of the printed surface occurs.
{circle around (5)} Also upon starting, even if the scuff rollers 92b and 92a are started at a sudden timing, the pinch rollers 93a and 93b do not rotate, and consequently, no stain to the print by rubbing of the printed surface occurs similarly. The sudden timing signifies that the velocity increases suddenly.
{circle around (6)} When backward transportation upon stopping of printing of the continuous recording paper 100 is performed or when the continuous recording paper 100 is transported in the reverse direction, since the pinch rollers 93a and 93b rotate together with the continuous recording paper 100, no stain to the print by rubbing of the printed surface occurs either.
Therefore, when single-sided printing is performed, no stain to the print occurs even if the continuous recording paper 100 is transported using the scuff rollers 92b and 92a. On the other hand, when double-sided printing is performed, during printing described in the paragraph {circle around (1)} above, since the velocity of the scuff rollers 92b and 92a is higher by approximately 5 to 30% than the transport velocity, the difference between the velocities is sufficiently small and no stain to the print occurs.
However, when double-sided printing is performed, since the scuff rollers 92b and 92a are used to transport the continuous recording paper 100, a surface of the continuous recording paper 100 which has been printed by the first printer 80a faces the scuff rollers 92b and 92a of the second turn bar 80b. Consequently a pressure called pinch pressure of each of the scuff rollers 92a and 92b is applied to the surface of the continuous recording paper 100 printed by the first printer 80a, and this pressure removes toner powder from the surface of the continuous recording paper 100 and causes stain to the print.
In particular, when the scuff rollers 92b and 92a are in such an idle rotation condition as described in paragraph {circle around (2)} above, since the velocity difference is as great as approximately 105% to 130%, a high pinch pressure is applied to the print and this causes stain to the print. Also while the continuous recording paper 100 is backwardly transported as in paragraph {circle around (3)} above, since the scuff rollers 92b and 92a are rotating forwardly, the velocity difference is as high as approximately 205% to 235% and this causes stain to the print.
Accordingly, the system described above has a subject to be solved in that, where it is used for double-sided printing, since a printed surface of the continuous recording paper 100 faces the scuff rollers 92b and 92a and the scuff transport velocity and the main transport velocity are different from each other, the printed surface is rubbed with the scuff rollers 92b and 92a and this deteriorates the picture quality of the print.
It is an object of the present invention to provide a double-sided printing apparatus of the type wherein two electrophotographic printers each including a tractor unit, a flash fixing unit and scuff rollers are connected to each other, and a double-sided printing method for the double-sided printing apparatus by which, even if a printed surface of continuous recording paper contacts with the scuff rollers, no stain to the print is caused by the scuff rollers.
In order to attain the object described above, according to the present invention, fixed acceleration control of the tractor units and the scuff rollers is performed, and a predetermined tension is applied to the continuous recording paper.
More particularly, according to an aspect of the present invention, there is provided a double-sided printing apparatus, comprising front surface printing means for printing on a front surface of a continuous medium and transporting the continuous medium in a printing transport direction, paper turning over means provided on the printing transport direction side of the front surface printing means for turning over the continuous medium to reverse the front and rear surfaces of the continuous medium and transporting the continuous medium in the printing transport direction, and rear surface printing means provided on the printing transport direction side of the paper turning over means for printing on the rear surface of the continuous medium and transporting the continuous medium in the printing transport direction, the rear surface printing means including main transport means for forming a print image on the rear surface of the continuous medium and transporting the continuous medium in the printing transport direction, fixing means provided on the downstream side of the main transport means in the printing transport means for fixing the print image formed on the continuous medium to the continuous medium, scuff transport means provided on the downstream side of the fixing means in the printing transport means for transporting the continuos medium in the printing transport means and outputting transport amount information, fixed acceleration control means for controlling the transport velocity of the main transport means and the transport velocity of the scuff transport means with fixed accelerations, and tension control means for controlling the main transport means and the scuff transport means so that the continuous medium may have a predetermined tension when printing of the continuous medium is started.
The double-sided printing apparatus is advantageous in that rubbing of the print on the continuous medium is eliminated and further in that, since the continuous medium is controlled to a state wherein it has a predetermined tension, stain to the print does not occur.
The tension control means may control the scuff transport means and the main transport means so that the main transport means is activated after a predetermined time after the scuff transport means is activated.
The tension control means may control the main transport means and the scuff transport means so that the scuff transport means is stopped earlier than the main transport means to generate a slack having a predetermined amount of the continuous medium and then the scuff transport means and the main control means are activated at the same timing to transport the continuous medium by a predetermined distance in a direction opposite to the printing transport direction to eliminate the slack generated on the continuous medium. In this instance, the tension control means may include feed amount management control means for determining the predetermined distance from the transport amount information outputted from the scuff transport means. And the tension control means may include slack amount detection means for detecting a slack amount of the continuous medium being transported between the main transport means and the scuff transport means to determine the predetermined distance.
With the double-sided printing apparatus, since the continuous medium is transported backwardly while it remains in a slackened state, there is an advantage that rubbing of the print on the continuous medium can be prevented.
According to another aspect of the present invention, there is provided a double-sided printing method, comprising a paper loading step of printing data to be printed on the front surface of a continuous medium, transporting the continuous medium in a printing transport direction, turning over the continuous medium to reverse the front and rear surfaces of the continuous medium and transporting the continuous medium in the printing transport direction, a scuff transport step of transporting the continuous medium with a fixed acceleration in the printing transport direction to take up the continuous medium which has a print image fixed to the rear surface thereof, a main transport step of forming a print image on the rear surface of the continuous medium after a predetermined time after the scuff transport step is started and transporting the continuous medium with a fixed acceleration in the printing transport direction, a detection step of detecting a slack amount of the continuous medium before the continuous medium being transported by the main transport step is stopped, and a paper tension keeping step of stopping, when the transportation in the printing transport direction is to be stopped, the scuff transportation after the slack amount detected by the detection step is eliminated after the main transportation is stopped and stopping, when the transportation in a direction opposite to the printing transport direction is to be stopped, the main transportation after the slack amount detected by the detection step is eliminated after the scuff transport is stopped.
The double-sided printing method is advantageous in that, even if a surface of a continuous medium printed by performing double-sided printing by means of two single-sided printing apparatus connected to each other in such a state that the scuff transport velocity and the main transport velocity are different from each other contacts with a scuff roller, no stain to the print from the scuff roller occurs, and consequently a print image of good quality can be obtained.
According to a further aspect of the present invention, there is provided a double-sided printing method, comprising a paper loading step of printing data to be printed on the front surface of a continuous medium, transporting the continuous medium in a printing transport direction, turning over the continuous medium to reverse the front and rear surfaces of the continuous medium and transporting the continuous medium in the printing transport direction, a scuff transport step of forming a print image on the rear surface of the continuous medium and transporting the continuous medium with a fixed acceleration in the printing transport direction, a main transport step of transporting the continuous medium, which has a print image fixed to the rear surface thereof, with a fixed acceleration in the printing transport direction simultaneously with the scuff transport step, a slack generating step of stopping the transportation of the continuous medium after the scuff transportation is stopped to generate a slack of the continuous medium, and a reverse transport step of transporting the continuous medium in a direction opposite to the printing transport direction at the same timing as the continuous medium is scuff transported in the direction opposite to the printing transport direction.
The double-sided printing method is advantageous in that a continuous medium can be transported stably from immediately after printing is started.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.